Traditionally, there are known piezoelectric generators that are vibrated by undergoing acceleration or distortion and generate electric power by the piezoelectric effect. When such piezoelectric generators are used as a power source, other power sources, such as batteries, are not necessary. Accordingly, these piezoelectric generators are suitably used as a power source for various sensors in applications subjected to vibration or distortion.
One example of the above piezoelectric generators is disclosed in PTL 1 below. FIG. 6 is a schematic partial cut-away front cross-sectional view that illustrates a piezoelectric generator described in PTL 1.
A piezoelectric generator 101 includes a substrate 102 made of silicon. A circular hole 102a is disposed in the upper surface of the substrate 102. An electrode 104 is disposed on the upper surface of the substrate 102. A discoid piezoelectric element 103 is fixed so as to close the circular hole 102a. The piezoelectric element 103 includes a piezoelectric plate 103a made of polyvinylidene fluoride, a first electrode 103b disposed on the upper surface of the piezoelectric plate 103a, and a second electrode 103c disposed on the lower surface thereof.
The second electrode 103c is electrically coupled to the electrode 104. An electrode 105 is disposed on the upper surface of the substrate 102 at a site spaced away from the electrode 104. The electrode 105 is electrically coupled to the first electrode 103b with a bonding wire 106.
A weight 107 is fixed to the upper surface of the piezoelectric element 103. When the piezoelectric generator 101 undergoes vibration accompanying acceleration or distortion, the portion to which the weight 107 is fixed vibrates in the directions indicated by the arrows. Charge based on this vibration is extracted from the first and second electrodes 103b and 103c. 
PTL 1 also describes a both-end support type piezoelectric generator as a modified example of the above-described piezoelectric generator 101. Although not individually illustrated, the both-end support type piezoelectric generator is described as having substantially the same cross-sectional structure as that of the piezoelectric generator 101 illustrated in FIG. 6. That is, the piezoelectric generator 101 uses the piezoelectric element 103 having a circular planar shape so as to close the circular hole 102a, whereas, for the both-end support type piezoelectric element, both ends of a rectangular piezoelectric element are fixed in a similar way to that illustrated in FIG. 6 such that the piezoelectric element is supported at the both ends.
PTL 1: Japanese Unexamined Patent Application Publication No. 7-107752
Traditionally, a piezoelectric generator that includes a piezoelectric element supported by a cantilever is known. For that piezoelectric generator, there is a problem in that the resonance frequency of vibration when, for example, acceleration is applied tends to vary.
In contrast to this, a piezoelectric generator including a piezoelectric element supported at both ends is considered to be able to reduce variations in the resonance frequency of vibration. However, in reality, for a piezoelectric generator that has a cross-sectional structure illustrated in FIG. 6 and that is a structure in which a piezoelectric element is supported at both ends, the resonance frequency tends to vary depending on conditions of installation, and the power generation efficiency also tends to vary.